feat(ms-ai-architect): Sesjon 3 - decision-ledger (lag 2) + discovery-dedup

Lukker discovery-løkken gjennom operatør-gaten. data/decisions.json er eneste
skrive-autoriserte bro mellom deteksjon og KB/registry; discovery LESER den og
utelater alt operatøren har tatt stilling til.

Dedup-policy = A (operatør-valg): isDecided = enhver ledger-entry (approved/
rejected/pending). Kun helt fraværende URLer re-foreslås.

- lib/decisions-io.mjs: createLedger/load/save(atomisk)/isDecided/recordDecision
  (ren)/filterUndecided. TDD: 10 tester før kode.
- discover-new-urls.mjs leser ledger, filtrerer, rapporterer deduped_by_ledger.
  Importerer ALDRI write-utils (invariant verifisert, 6 guard-tester).
- Gate dokumentert i kb-update.md §3b (eneste skrivevei).
- decisions.json tracket via gitignore-negasjon (som domain-taxonomy.json).

Kriterium møtt: dedup-diff (rejected re-foreslås ikke runde 2).
Tester: validate 239 · kb-update 82 (+16) · kb-eval 13 · kb-integrity 115/115.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01REiKFhP4w6xGXXqWKpPCJJ

.gitignore

@@ -23,9 +23,10 @@ node_modules/
 .work/
 org/
 # Generated KB-update artifacts (registry, reports) are ignored, but the
-# hand-authored taxonomy (single source of truth, lag 0) is tracked.
+# hand-authored taxonomy (lag 0) and the decision ledger (lag 2) are tracked.
 scripts/kb-update/data/*
 !scripts/kb-update/data/domain-taxonomy.json
+!scripts/kb-update/data/decisions.json
 .kb-backup/
 .rollback-in-progress